1. Field of the Invention
The invention relates to foam vessels for cryogenic fluid storage and separation.
2. Description of Related Art
Cryogenic fluids, such as liquid nitrogen, liquid oxygen, and liquid hydrogen have found a vast number of scientific and other applications. These fluids are extremely cold (liquid nitrogen, for example, boils at about −196° C.) and are used, for example, in biological specimen preparation and preservation, x-ray crystallography sample preparation, environmental testing, and general refrigeration, to name a few. Liquid nitrogen, in particular, is nearly ubiquitous in most modern laboratories.
Storing cryogenic fluids poses its own set of problems, not the least of which is minimizing heat transfer into and out of the fluid. The original cryogenic storage vessels were the work of Sir James Dewar, and are named in his honor. The classic Dewar is a double vessel with a glass inner wall, an outer wall, and an evacuated space between the inner and outer walls that reduces heat transfer by conduction. The glass may be silvered to reduce heat transfer by radiation, and an outer layer of metal is sometimes provided.
There are four major problems with classic Dewars. First, if the Dewar is dropped during handling, there is a risk that the glass will shatter. Second, the glass material has a large thermal mass, which means that a relatively large amount of cryogenic fluid will boil off and be lost in cooling the Dewar to the appropriate temperature when fluid is first placed in the Dewar for storage. Third, the cost of a traditional Dewar is high. (For example, at the time of writing, a 600 mL Dewar sold by Hampton Research of Aliso Viejo, Calif. has a retail price of $197.) Finally, the classic Dewar is not necessarily easy to handle.
Occasionally, thin-walled polystyrene foam containers, such as STYROFOAM® coffee cups, have been used to hold liquid nitrogen temporarily during use. However, polystyrene vessels of this type often cause the liquid nitrogen to boil off relatively rapidly. Moreover, these sorts of vessels are not mechanically robust and tend to fail easily.